Multiple stayout zones for ground-based bright object exclusion

ABSTRACT

A vehicle ( 12 ) including a control system ( 18 ) is used for controlling vehicle attitude or angular velocity ( 38 ). The processor ( 24 ) is coupled to a star sensor or tracker ( 22 ) and a memory ( 30 ) that may include a star catalog ( 32 ), and an exclusion list ( 36 ). The exclusion list ( 36 ), a list of stars to be temporarily excluded from consideration when determining attitude or angular velocity or relative alignment of star sensors or trackers, is calculated on board. Such a calculation prevents the necessity for a costly, periodic, ground calculation and upload of such data. By manipulating the star catalog, or sub-catalogs derived from said catalog, based upon the exclusion list ( 36 ), measurements of such excluded stars are prevented from corrupting the attitude or angular velocity or alignment estimates formulated on board. The system uses multiple stayout zones for excluding stars from the exclusion list. A central exclusion zone excludes all stars while a second or more exclusion zones allow some stars to be used in the attitude determination

FEDERAL RESEARCH STATEMENT

This invention was made with Government support. The Government hascertain rights in this invention.

BACKGROUND OF INVENTION

The present invention relates generally to attitude or angular velocityor sensor alignment estimate adjustment for a vehicle, and moreparticularly, to algorithms involving attitude or angular velocity orsensor alignment determination, using star position measurements andusing multiple exclusion zones.

Satellites and other vehicles are in widespread use for various purposesincluding scientific research and communications. Many scientific andcommunications missions, however, cannot be accurately fulfilled withoutconsistently monitoring and controlling the 3-axis attitude and angularvelocity of the vehicle. In many applications, the vehicle must beoriented to transmit signals in particular directions or to receivesignals from specifically located sources. Furthermore, in such asituation, the vehicle angular velocity must be such so as to maintainthe desired orientation, over time. Without accurate control overvehicle 3-axis attitude and angular velocity, the transmission orreception of such signals is hindered and at times impossible.

Such control requires systems for 3-axis attitude and angular velocitydetermination, which generally include one or more star trackers and a3-axis gyroscope. During normal operation, star trackers or star sensorsprovide attitude-related information and the 3-axis gyroscope is neededto provide angular velocity information. As there are inherent, andtime-varying, errors from star trackers, star sensors, and gyros, it isoften necessary to constantly estimate such errors, in order tocompensate for them. One common method of doing so is to correlate startracker or sensor position measurements of stars with known positions ofthe same stars, as listed in a star catalog, or database. Discrepanciesbetween the measured and predicted positions allow direct estimation oftracker error, and indirect estimation of gyro error. Knowing sucherrors allows estimation of attitude or angular velocity, or refinementof existing estimates. Furthermore, if there are multiple star trackersor star sensors on-board, such correlations allow determination of thealignment of such trackers or sensors, with respect to each other; suchdetermination yields greater accuracy in future attitude and angularvelocity estimates.

Stellar Inertial Attitude Determination (SIAD) algorithms employ acarefully designed star catalog or database for selection andidentification of stars tracked by star trackers or star sensors. Thecurrent known art in star selection for star trackers mainlyconcentrates on generating star catalogs with certain properties.Typically, one method of locating entries in a star catalog thatcorrespond to stars in a tracker field of view (FOV) uses a standardbinary search that is sorted by declination only. This method is notvery efficient because it involves searching through hundreds of entriesto find the stars that are located within the FOV.

Various other methods involve generation of multiple overlappingsub-catalogs that contain stars for a specific FOV in the sky. At anypoint in time, the stars within a star tracker's FOV will reside in oneor more of these sub-catalogs. Each star catalog entry that isrepresented in a FOV sub-catalog has been determined, using on-boardprocessing, to be in the tracker FOV.

In a SIAD algorithm, the entries corresponding to stars intruded bybright objects such as planets, asteroids, or comets, need to beexcluded from the star catalog or sub-catalog, i.e., excluded fromconsideration by the algorithm. This is so that bright objects are notmistaken for stars, or the light from the objects does not corrupt themeasurements made by the star sensor. Traditional object-based catalogentry exclusion is performed on the ground. These stars intruded byplanets or other bright objects are excluded from a revised copy of theon-board star catalog. The revised star catalog is then uploaded to thespacecraft control processor (SCP). The uploading is time-consuming andmay easily be interrupted. This may cause delays in the proper attitudedetermination or errors in the on-board version of the catalog.

Traditionally, there is only one stayout zone for each object in theexclusion algorithm. All the stars inside the stayout zone are excludedfrom the star catalog so that the bright planet/object will not bemistaken as a star during attitude determination. The exclusion zonesmay be excessively large and over-inclusive. The number of starsexcluded may be such that attitude determination performance may bereduced.

It would therefore be desirable to provide a system that decreases thenumber of excluded stars to improve the performance of the attitudedetermination system.

SUMMARY OF INVENTION

The present invention improves the performance of the attitudedetermination system by allowing less stars to be excluded by thespacecraft in the exclusion system.

In one aspect of the invention a method of operating a star trackerincludes determining multiple stayout zones for an object, selecting afirst stayout zone from the multiple stayout zones, determining a starin the first stayout zone, and determining a vehicle inertial attitudeor angular velocity based on star measurements of sensed or trackedstars, excluding the star within the first stayout zone.

In a further aspect of the invention, a vehicle includes an attitude orangular velocity control system, a star tracker having a field of view,and a star catalog memory having a star catalog stored therein. The starcatalog has a plurality of entries, each entry having an associated flagtherewith. The spacecraft further includes an exclusion list memory. Aprocessor is coupled to the attitude or angular velocity control system,the star tracker, the star catalog memory, and the exclusion listmemory. The processor determines multiple stayout zones for an objectand selects a stayout zone from the multiple stayout zones. Theprocessor further determines a plurality of objects in the stayout zoneexcluding at least one of the objects from the field of view within thestayout zone to form a revised a database, star catalog or starsub-catalog. The processor determines a vehicle inertial attitude,angular velocity, relative star sensor or tracker misalignment estimatein response to the revised database, star catalog, or star sub-catalogand controls the attitude control system or angular velocity system inresponse to the revised database, star catalog, or star sub-catalog.

One advantage of the invention is that by providing multiple stayoutzones, the amount of stars excluded may be reduced to improve theattitude determination performance.

Other aspects and advantages of the present invention will becomeapparent upon the following detailed description and appended claims,and upon reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a set of vehicles (depicted as asatellite system, in accordance with the preferred embodiment of thepresent invention) for determining stars in a star tracker field ofview;

FIG. 2 is a block diagram of an apparatus for determining stars in astar tracker field of view in accordance with the preferred embodimentof the present invention; and

FIG. 2A is a block diagram of a control circuit for the ground station.

FIG. 3 is a diagrammatic view of a star catalog.

FIG. 4 is a flow chart of a first embodiment of a method for determiningstars in a star tracker field of view in accordance with the preferredembodiment of the present invention.

FIG. 5 is a flow chart of a second embodiment of a method fordetermining stars in a star tracker field of view in accordance with thepreferred embodiment of the present invention.

FIG. 6A is one example of multiple stayout zones including two circularstayout zones.

FIG. 6B is an example of three stayout zones as the multiple stayoutzones which are rectangular.

FIG. 6C is a third embodiment of a multiple stayout system includingthree different types of stayout zones including circular, elongated andrectangular.

FIG. 7 is a flow chart illustrating a method of operating a system usingmultiple stayout zones.

DETAILED DESCRIPTION

In the following figures the same reference numerals will be used toidentify the same components.

The present invention is described with respect to a star catalog, orsub-catalog, entry exclusion system for a vehicle. It should be notedthat various types of vehicles may benefit from the exclusion system. Itshould also be noted that the exclusion system is not limited toexclusions due to the effects of planets. Rather, various objects suchas planets, asteroids, comets, other extraterrestrial objects, or othervehicles, may be the cause of exclusion. Also, gyros or otherinformation may be used in addition to star catalog/stay out zonecalculations.

Referring to FIG. 1, a perspective view of a system 10 for determiningstars in a star tracker field of view (FOV) in accordance with oneembodiment of the present invention is illustrated. The system 10 iscomprised of one or more vehicles 12. The system may also be incommunication or coupled to a ground station 14 through signals 13. Theground station 14 may include control circuitry 15 used to determinedthe stay out zones. The ground station 14 may include various types ofground based stations including but not limited to a network operationcenter, a control center, or the like. Each vehicle 12 includes anapparatus 18 for determining inertial attitude based upon a plurality ofstars 20. The vehicle 12 may be one of various types of vehicles,including satellites and other spacecraft.

The apparatus 18 is responsible for locating stars 20 within or near astar tracker field of view in order to control the attitude or angularvelocity of vehicle 12. Many scientific and communications missionscannot be accurately fulfilled without consistently monitoring andcontrolling the vehicle 3-axis attitude or angular velocity. In manyapplications the vehicle must be positioned to transmit signals inparticular directions or to receive signals from specifically locatedsources. Without accurate control over vehicle 3-axis attitude andangular velocity, the transmission or reception of such signals ishindered and at times impossible.

Referring to FIG. 2, a block diagram of apparatus 18 for determiningstars 20 within or near a star tracker field of view 28 in accordancewith one embodiment of the present invention is illustrated. Apparatus18 includes a star tracker or star sensor 22 and a processor 24.Apparatus 18 also includes a memory 30 that includes a star catalog 32,and an exclusion list 36. The processor 24 may also be coupled to anattitude or angular velocity control system 38.

Star tracker 22 is mounted to the vehicle 12 and is coupled to processor24 in a conventional manner. Star tracker 22 includes a field of view(FOV) 28 and a boresight 40 in the FOV 28. Star tracker 22 is used tosense a plurality of positions, relative to star tracker 22, of aplurality of stars 20. Star tracker 22 then generates a plurality ofsignals corresponding to the plurality of star positions in the FOV 28.It should be noted that more than one star tracker 22 may be included ona vehicle. The present invention allows determination of multiple startrackers with respect to the others when multiple star trackers areused.

Processor 24 may be an individual processor or may be comprised of aplurality of processors. For example, star tracker 22 may include itsown processor. Likewise, attitude or angular velocity control system 38may also comprise its own processor such as a spacecraft controlprocessor (SCP). For simplification purposes the processor isillustrated as a single component. Each processor may bemicroprocessor-based. Processor 24 resides in vehicle 12. Processor 24is coupled to star tracker 22 and receives the plurality of signalscorresponding to the plurality of star positions in the FOV 28.Processor 24 provides control logic operative to select at least one ofthe plurality of signals corresponding to the positions of one or morestars. Processor 24 uses star catalog 32 to determine which stars 20 toselect or determine the stars' positions with respect to theEarth-Centered Inertial (ECI) frame.

Memory 30 is illustrated as a plurality of separate elements. Thoseskilled in the art will recognize that the memory may comprise a singlememory system. It should also be noted that if a microprocessor is usedfor processor 24 that the microprocessor may include memory therein. Thememory may include various types of memory including but not limited torandom access memory (RAM).

The attitude or angular velocity control system 38 may comprise aplurality of thrusters and momentum wheels as will be evident to thoseskilled in the art. The attitude or angular velocity control system 38controls the various momentum wheels or thrusters to orient the vehiclein its desired direction.

An antenna 41′ may be coupled to processor for sending and receivingvarious control signals and/or calculations to ground station 14.

Referring now to FIG. 2A, the control circuitry 15′ may also performexclusion as described below. The control circuitry 15′ may includesimilar elements to that of the vehicle. Each similar element has beenprimed. That is, a star catalog 32′ and exclusion list 36′ are coupledto a processor 24′. An antenna 41′ may be used to communicate varioussignals to vehicle 12.

Referring now to FIG. 3, a simplified database, star catalog orsub-catalog 32 is illustrated. Each entry in catalog or sub-catalog 32may include associated star information and may also include aninclude/exclude flag 46. The include/exclude flag may, for example, beimplemented as a binary zero or one. For illustration purposes an “I”for include and an “E” for exclude have been used. The processor 24, aswill be further described below, may be programmed to change theinclude/exclude flag 46 to a desired state. That is, processor 24 maychange the flag 46 to include from exclude or to exclude from include(flagging). Star catalog 32 may also consist of a plurality ofinformation including but not limited to star right ascension anddeclination angles in a given ECI frame, star instrument magnitude, andother star properties. Star catalog 32 may contain data that is storedusing primary and multiple secondary arrays. It should also be notedthat various numbers of stars may be included in the catalog.

Referring to FIG. 4, a flow chart of a method of a first embodiment of amethod according to the present invention is illustrated. It should benoted that the method may take place on board the vehicle or on theground. Various steps may be performed in either location andcommunicated to the other location. In step 58, the include/excludeflags associated with each star catalog or sub-catalog entry are set toinclude. In step 60 a stayout zone, associated with a bright object, isdetermined. The stayout zone may, for example, be a regular shape suchas a rectangular or square field of view. The stayout zone may also bevariable in size and may also be round or oblong. The properties of thestayout zone may be a function of the object position and magnitude;they may also depend on various other parameters, such as magnitude andposition of the stars within the zone. In step 62 the determination ofwhich stars are inside the stayout zone of the bright object or planetis made. In step 64 the stars to be excluded are listed in the exclusionlist. In step 66 the stars in the exclusion list are flagged as excludedby switching the include/exclude flag of the corresponding star catalogor sub-catalog entries to exclude.

In step 68, based on star sensor measurements of the positions of starslisted in the star catalog or sub-catalog, and flagged as included, thespacecraft inertial attitude estimate or angular velocity estimate isdetermined or refined. In step 70, the attitude is controlled to orientthe spacecraft as desired, or the angular velocity is controlled tomaintain the desired attitude over time. Other considerations such asvehicle gyros such as 3-D gyros may also be taken into consideration.

It should be noted that the steps described above may all be performedon the spacecraft. This prevents problems due to timing and errors dueto the transmission of the information from a ground station.

Referring now to FIG. 5, the same process described above with respectto FIG. 4 may be used for multiple planets or objects. N is defined asthe number of objects.

The configuration is nearly identical in that step 58′ initializes allstar catalog or sub-catalog include/exclude flags to include, step 60′determines a stayout zone for bright object x, where x was set to 1 instep 59′, step 62′ calculates the stars inside the stayout zone ofbright planet/object x, step 64′ lists the stars to be excluded in anexclusion list.

Step 66′ excludes the stars in the exclusion list from consideration inattitude or angular velocity estimate formulation by switchinginclude/exclude flags of the corresponding star catalog entries toexclude.

In step 67′, x is replaced with (x+1). In step 67″, should the new valueof x be less than or equal to N, the procedure returns to step 60′, todetermine exclusions due to object x. Should the value of x be greaterthan N, in step 68′, the spacecraft attitude or angular velocity orrelative star sensor or tracker alignments may be determined after thestar catalog exclusions due to the last planet/object N are determinedin step 66′. Likewise, in step 70′, the attitude or angular velocity maybe controlled only after the attitude or angular velocity is determined.

It should be noted that the present invention may be used autonomouslyto perform realtime exclusion. Also, periodic maintenance for all theplanets/objects may be performed or individually performed. The excludedstar list may also be stored as part of a whole list or an individuallist corresponding to the planet/object.

Referring now to FIG. 6A, multiple stayout zones may be used in theexclusion determination. The stayout zones may be multiple shapes andmultiple sizes. Also, multiple numbers of stayout zones such as two,three, four, etc. may be used. By using multiple stayout zones, thenumber of stars used for attitude determination may be increased.

As shown in FIG. 6A, a first stayout zone 80 circular in shape isillustrated. A second stayout zone 82 is concentric with the firststayout zone. As will be further described below, the first stayout zone80 may have all stars excluded from therein. In stayout zone 82, onlystars that are dimmer than a first threshold may be excluded.

Referring now to FIG. 6B, three stayout zones are provided. The centerrectangular stayout zone 84, a second stayout zone 86 that forms anannular band around the first stayout zone, and a third rectangularstayout zone 88 is also illustrated. In the first stayout zone 84, allthe stars may be excluded. In stayout zone 86, only stars dimmer than afirst threshold may be excluded from this annular band. In stayout zone88 which forms an annular band around stayout zone 86, only stars thatare dimmer than a second threshold may be excluded. As illustrated inFIG. 6B, each of the stayout zones may be rectangular or square inshape.

Referring now to FIG. 6C, three differently shaped stayout zones may beprovided. The first stayout zone 90 corresponds to an area where allstars are excluded there from. Stayout zone 90 is elliptical or oval inshape. The elongated shape corresponds to a column within a CCD of thestar tracker. A second stayout zone 92 having first stayout zone 90therein excludes stars that are dimmer than a first threshold. A thirdstayout zone 94 is elongated in the direction of axis 91. The stayoutzone 94 is rectangular in shape. The rectangle is narrower, in thisexample, than the width of stayout zone 92.

One reason for providing an elongated stayout zone is the deleteriouseffects of bright objects on the sensors in the star trackers. An effectknown as CCD array blooming forms a highly asymmetric image thattypically occurs along the readout column direction of the sensor with arectangular field of view. Prior knowledge of the intended pointingdirection of the star tracker may allow a suitably restrictive yetoverly conservative stayout zone in the star catalog. Depending on theapplication, this region need not guarantee non-interference, but simplyreduce the probability of interference. Other uses of non-circularstayout zone shapes is for inherently non-circular objects such as comettails.

Further, a spacecraft typically operates in three different scenarios.That is, the satellite may have no attitude knowledge, rough attitudeknowledge, or priority attitude knowledge. The present invention iscapable of worse scenario no attitude knowledge. The circular stayoutzones are typically useful for any application in any of the abovementioned scenarios, particularly no attitude knowledge. Once someattitude knowledge is obtained, the stayout zones may be reduced in oneor both horizontal and vertical directions to increase the number ofstars available for attitude determination. Rectangular stayout zones ora combination circular and rectangular zones may be performed on orbit.However, these zones are particularly useful for exclusion performed onthe ground, when rough attitude information is available. The starsinside the part or whole rectangular field of view of the star sensorcan be excluded based on the spacecraft nominal steering profile inorder to avoid the CCD array blooming problem. The star catalog may thenbe uploaded from the ground to the spacecraft.

Referring now to FIG. 7, a method of operating a system using multiplestayout zones is illustrated. Again, the calculations may be performedon the ground or on the vehicle. In step 100 the boundaries of multiplestayout zones for a particular object is determined. As mentioned above,the multiple stayout zones may be of various shapes, sizes and numbers.The present example is set forth with three stayout zones. However, two,three, four, etc. may be provided. In step 102 if the star is within theinnermost stayout zone, step 104 excludes the star from the stayoutzone. Step 100 may then be executed for a different bright object.

Referring back to step 102, if the star is not within the innermostzone, step 106 determines whether the star is within a second zoneoutside of the first zone. If the star is outside of the first zone andwithin the second zone, step 108 is executed. If the magnitude of thestar is less than a first threshold in step 108 the star is excluded instep 110. In step 108, if the star is not less than a first threshold orafter step 110, step 100 is excluded for a different star for adifferent object.

Referring back to step 106, if the star is not within a secondthreshold, step 112 determines whether the star is within a third zoneoutside of the second zone. If the star is within the third zone, step114 is executed. In step 114, if the magnitude of the star is less thana second threshold, step 116 excludes the star from the star catalog. Instep 114 if the magnitude of the star is not less than the secondthreshold and after step 116, step 100 is executed for a different starfor a different object.

Referring back to step 112, if the star is not within the third zone,step 100 is again executed.

The above method is suitable for objects of magnitude of +1 or brighter.Typically, objects with a stellar magnitude of +1 or brighter areignored with a singular circular stayout zone of 0.5 degrees. Objectsthat may reach a magnitude of +1 or brighter may include Mars, Jupiter,Venus, Saturn, Uranus, and Neptune. Further, the small central stayoutzone provides complete exclusion while a larger region includes starsthat were excluded in prior systems. Thus, more stars are available forattitude determination.

While the invention has been described in connection with one or moreembodiments, it should be understood that the invention is not limitedto those embodiments. On the contrary, the invention is intended tocover all alternatives, modifications, and equivalents, as may beincluded within the spirit and scope of the appended claims.

1. A method of operating a star tracker comprising: in a ground station,determining multiple stay out zones for an object; in a ground station,selecting a first stay out zone from the multiple stay out zones;determining a star in the first stayout zone; and determining a vehicleinertial attitude or angular velocity, based on star measurements ofsensed or tracked stars, excluding the star within the first stayoutzone.
 2. A method as recited in claim 1 wherein determining multiplestayout zones comprises calculating at least one circular stayout zone.3. A method as recited in claim 1 wherein determining multiple stayoutzones comprises calculating at least one non-circular stayout zone.
 4. Amethod as recited in claim 1 wherein determining multiple stayout zonescomprises calculating at least one non-circular stayout zone and onenon-circular stayout zone.
 5. A method as recited in claim 1 whereinexcluding the star is performed for a fixed period of time.
 6. A methodas recited in claim 1 wherein excluding the star is performed for anon-fixed period of time.
 7. A method as recited in claim 1 whereinexcluding the star is dependent on properties of the star and propertiesof the object.
 8. A method as recited in claim 7 wherein the property isbrightness.
 9. A method as recited in claim 1 wherein further comprisingcontrolling vehicle attitude or angular velocity, in response to thevehicle inertial attitude or angular velocity.
 10. A method as recitedin claim 1 wherein excluding the star is performed on-board the vehicle.11. A method as recited in claim 1 wherein selecting comprises when astar is within the first exclusion zone, excluding the star, when thestar is in a second exclusion zone of the multiple exclusion zones,excluding the star when the brightness is below a first magnitude.
 12. Amethod as recited in claim 11 wherein the first exclusion zone has adifferent shape than the second exclusion zone.
 13. A method as recitedin claim 11 further comprising when the star is in a third exclusionzone of the multiple exclusion zones, excluding the star when thebrightness is below a second magnitude, different than the firstmagnitude.
 14. A method as recited in claim 13 wherein the thirdexclusion zone has a different shape than the first exclusion zone orthe second exclusion zone.
 15. A method of determining a vehicleattitude or angular velocity, comprising: in a ground station,calculating multiple stayout zones associated with a bright object, or aplurality of objects; in a ground station, selecting a one stay out zonefrom the multiple stay out zones; calculating the stars inside thestayout zone intruded by a bright object therein; listing the starsinside the stayout zone in an exclusion list; flagging star catalog ordatabase entries, corresponding to stars listed on the exclusion list,as excluded from consideration by an attitude determination algorithmand procedure or a angular velocity determination algorithm andprocedure; and determining a vehicle inertial attitude or angularvelocity, in response to data including star position measurements andthe star catalog.
 16. A method as recited in claim 15 whereindetermining multiple stayout zones comprises calculating at least onecircular stayout zone.
 17. A method as recited in claim 15 whereindetermining multiple stayout zones comprises calculating at least onenon-circular stayout zone.
 18. A method as recited in claim 15 whereindetermining multiple stayout zones comprises calculating at least onenon-circular stayout zone and one non-circular stayout zone.
 19. Amethod as recited in claim 15 wherein excluding the star is performedfor a fixed period of time.
 20. A method as recited in claim 15 whereinexcluding the star is performed for a non-fixed period of time.
 21. Amethod as recited in claim 15 wherein excluding the star is dependent onproperties of the star and properties of the object.
 22. A method asrecited in claim 21 wherein the property is brightness.
 23. A method asrecited in claim 15 wherein further comprising controlling vehicleattitude or angular velocity, in response to the vehicle inertialattitude or angular velocity.
 24. A method as recited in claim 15wherein excluding the star is performed on-board the vehicle.
 25. Amethod as recited in claim 15 wherein selecting comprises when a star iswithin the first exclusion zone, excluding the star, when the star is ina second exclusion zone of the multiple exclusion zones, excluding thestar when the brightness is below a first magnitude.
 26. A method asrecited in claim 25 wherein the first exclusion zone has a differentshape than the second exclusion zone.
 27. A method as recited in claim25 further comprising when the star is in a third exclusion zone of themultiple exclusion zones, excluding the star when the brightness isbelow a second magnitude, different than the first magnitude.
 28. Amethod as recited in claim 27 wherein the third exclusion zone has adifferent shape than the first exclusion zone or the second exclusionzone.
 29. A system comprising: a vehicle comprising, an attitude controlsystem or angular velocity control system; a star tracker having fieldof view; a ground station comprising, a star catalog memory having astar catalog stored therein said star catalog having a plurality ofentries, each entry having an associated flag therewith; an exclusionlist memory; and a processor coupled to said attitude or angularvelocity control system and said star catalog, said exclusion listmemory, said processor determining multiple stay out zones for anobject, selecting a stay out zone from the multiple stay out zones,determining a plurality of objects in the stayout zone, excluding atleast one of the objects from the field of view within the stayout zoneto form a revised database, star catalog, or star sub-catalog,determining a vehicle inertial attitude, angular velocity, relative starsensor or tracker alignment estimate, in response to the reviseddatabase, star catalog, or star sub-catalog and controlling the attitudecontrol system or angular velocity system in response to the reviseddatabase, star catalog, or star sub-catalog.
 30. A system as recited inclaim 29 wherein the vehicle comprises a spacecraft.
 31. A system asrecited in claim 29 wherein said multiple stayout zones comprisescalculating at least one circular stayout zone.
 32. A system as recitedin claim 29 wherein said multiple stayout zones comprises calculating atleast one non-circular stayout zone.
 33. A system as recited in claim 29wherein said multiple stayout zones comprises calculating at least onecircular rectangular stayout zone.
 34. A system as recited in claim 29wherein said multiple stayout zones comprises calculating at least onecircular stayout zone and one non-circular stayout zone.
 35. A system asrecited in claim 29 wherein excluding the star is dependent onproperties of the star and properties of the object.
 36. A system asrecited in claim 35 wherein the properties of the star and properties ofthe object comprise brightness.
 37. A system as recited in claim 29wherein selecting comprises when a star is within the first exclusionzone, said processor excluding the star, when the star is in a secondexclusion zone of the multiple exclusion zones, said processor excludingthe star when the brightness is below a first magnitude.
 38. A system asrecited in claim 37 wherein the first exclusion zone has a differentshape than the second exclusion zone.
 39. A system as recited in claim37 further comprising when the star is in a third exclusion zone of themultiple exclusion zones, said processor excluding the star when thebrightness is below a second magnitude, different than the firstmagnitude.
 40. A system as recited in claim 39 wherein the thirdexclusion zone has a different shape than the first exclusion zone orthe second exclusion zone.